This relates to the elimination of cardiac arrhythmia, particularly, atrial flutter by interrupting signals crossing the so-called isthmus region of the heart through electrophysiological (EP) treatment.
Cardiac arrhythmia presently affects approximately 2 million people in the United States alone. A first type of arrhythmia, atrial fibrillation, is the disorganized depolarization of a patient""s atrium, with little or no effective atrial contraction. Various uncoordinated stages of depolarization and repolarization, due to multiple reentry circuits within the atria, cause, instead of intermittent contraction, quivering in a chaotic pattern that results in an irregular and often rapid ventricular rate. A second type, atrial flutter, is a condition in which atrial contractions are rapid (250 to 300 beats per minute), but regular. In many instances, a circus movement caused by reentry is probably present. The condition is such that the ventricles are unable to respond to each atrial impulse so that at least a partial atrioventricular block develops. Either condition may be chronic or intermittent. It is atrial flutter that the present invention is most intended to address.
Prior methods for treating a patient""s arrhythmia include the use of antiarrhythmic drugs such as sodium and calcium channel blockers or drugs which reduce the Beta-adrenergic activity. Other methods include surgically sectioning the origin of the signals causing the arrhythmia, or the conducting pathway for such signals. However, the surgical technique is quite traumatic and is unacceptable to a large number of patients. A more frequently used technique to terminate the arrhythmia involves destroying the heart tissue which causes the arrhythmia by heat, e.g., applying a laser beam or high frequency electrical energy, such as RF or microwave, to a desired arrhythmogenic site on the patient""s endocardium. In the latter method, intravascular (EP) devices can be used to form contiguous lesions within a patient""s atrial chamber to provide results similar to the surgical segregation techniques in terminating the arrhythmia but with significantly reduced trauma.
Typically, an EP device is advanced within a patient""s vasculature and into a heart chamber and a lesion is formed at the site of interest when RF electrical energy is emitted from electrodes of the device. RF ablation techniques produce lesions of a generally small area. Consequently, several lesions are typically needed to completely ablate the area of the average arrhythmogenic site. As such, a major problem of RF ablation techniques is forming a lesion of the requisite size, which completely ablates the area of interest but does not unnecessarily destroy surrounding healthy tissue. There has been a need for ablation devices which allow for improved monitoring of the creation of a lesion, to generate linear lesions of a requisite length. The present invention satisfies this need.
It is well known that in order to effectively produce lesions using EP devices that contact with or proximity to target tissues is key. Various devices used to improve contact with sites of interest in the heart other than the isthmus region are known in the art. Basket-shaped or volume filling devices like basket-shaped catheters which expand to contact opposing heart wall sections, such as that disclosed in U.S. Pat. Nos. 5,228,442 and 5,908,446 to Imran and U.S. Pat. No. 5,465,717 to Imran et al., are known. Another device to provide efficient contact between the treatment device and a site of interest is disclosed in U.S. Pat. No. 5,482,037 to Borghi where a catheter having an electrode on a flexible member which is shaped by a control wire forms a manipulable unit adapted to achieve configurations advantageous for providing a section capable of improved contact of the electrode with tissue. U.S. Pat. No. 5,879,295 to Li et al. discloses a device having multiple electrodes that may be manipulated in a similar manner, except that the two control wires are connected apart from each other near the distal end of the device. Such a configuration allows for the formation of more complex shapes in using the device. Further, U.S. Pat. No. 5,895,417 to Pomeranz et al. discloses a catheter having a resilient, looped end with a section with electrodes. Either end of the loop may be advanced or drawn back to provide various shapes in order that the effective section of the catheter may better conform to a region. The non-active section of the loop may be used to bias the loop against a wall opposite the ablating electrodes portion to press the electrodes into improved contact with the wall it abuts.
Also, steerable or deflectable tip catheters and catheters with preformed curved sections that may be straightened for delivery purposes have been used to provide an electrode interface region conformable with particular regions in the heart. EP devices having simple J or C-shaped curved sections are known. U.S. Pat. No. 5,170,787 to Lindegren discloses a catheter utilizing a J-shaped preformed wire wherein the device has an ablating electrode at the tip. Also, there are EP devices where the curved shape is extended. U.S. Pat. Nos. 5,673,695 and 5,860,920 to McGee et al. disclose a device with a generally-circular or pigtail electrode array that may conform to the circumferential geometry of a selected annulus region in the heart. Both preformed and deflectable means of achieving the desired shape are disclosed therein. U.S. Pat. No. 5,462,545 to Wang et al. discloses a device having electrodes where the device may be formed in a planar spiral and a corkscrew configuration in addition to a generally circular shape. Further, U.S. Pat. No. 5,823,955 to Kuck et al. discloses an EP device with a distal end portion curving in one direction and switching back in an opposite direction. In all, such shapes are provided to enable improved accessibility to and/or interface with a treatment site in the heart.
The present invention also addresses the need for improved accessibility to and/or interface with the heart wall. However, the present invention meets the challenges presented in the treatment of arrhythmia by forming lesions between the tricuspid annulus and the inferior vena cava, i.e., in the xe2x80x9cisthmusxe2x80x9d region of the heart. Such lesions may be highly effective in treating atrial flutter by breaking abnormal circuits. While the isthmus has become an area of increasing interest, treating the region is complicated by the irregularity of the anatomical geometry and variation of the region from one patient to another. Ridges, crevasses, bumps and the like make uniform contact with the atrial wall for ablation and/or mapping in this region difficult. None of the devices noted above can perform effectively in RF ablation of the isthmus region.
The present invention provides a device and methods specifically adapted to face the challenges in ablating the isthmus region. An EP device utilizing variations on a shape having particular functional advantages is provided. The advantageous shape of the device allows it to be manipulated in a new manner which forms part of the invention.
This invention is directed to a electrophysiology (EP) device suitable for mapping functions and/or forming ablations or lesions in the isthmus region of a human patient""s heart. The EP device of the invention has electrodes along the outer surface of the device and may have temperature sensors to work in concert with the electrodes. When prepared for use the catheter-like device assumes a shape specialized to advantageously interface with the isthmus region to form lesions. Lesions formed may be made in the form of linear ablations particularly suitable for eliminating or minimizing atrial flutter and/or fibrillation by isolating sections of the patient""s atrial wall.
The EP device of the invention generally comprises an elongated shaft having a lumen and a proximal section, a distal section, and a plurality of at least partially exposed electrodes disposed on an outer surface of the distal section. A pre-formed forming member is provided in the lumen to shape the distal section of the device transition. Generally, the distal section is shaped in the form of a modified or flattened pigtail configuration with at least a terminal anchor region, and an intermediate interface region. A plurality of electrodes are spaced along a length of the interface section. Also, a tip may be provided at the end of the anchor region. The tip may be any typical atraumatic tip or a smooth, rounded member preferably comprising a radiopaque material. As with the electrodes, the tip may be connected to an electrical energy source to form an active or xe2x80x9chotxe2x80x9d member to serve as an ablating electrode.
The electrodes on the distal shaft section form a lesion from within a patient""s heart chamber when electrical energy, preferably RF energy, is emitted therefrom. The electrodes may be combination sensing and ablation electrodes which are capable of ablation and detection of electrical activity from within the patient""s body. In a preferred embodiment, the electrodes on the device (including the tip, if desired) are independent, for monopolar mode use with an electrode in contact with the exterior of the patient""s body for ablation. Alternatively, the electrodes may be configured in a bipolar mode for use as pairs of sensing electrodes on the shaft. A presently preferred electrode is in the form of a helical coil for improved device flexibility, although other designs are suitable including cylindrical bands, arcuate bands, strands, ribbons or the like. For high resolution sensing, the electrodes on the interface section or region may be spaced in a compact array. For sensing or ablating regions other than those opposing the interface region, additional electrodes, possibly closely packed, may be provided on the catheter as well.
A presently preferred embodiment of the invention includes at least one temperature sensor provided to monitor lesion formation placed between adjacent electrodes. To form an effective lesion in the tissue of the heart, the tissue generally should reach a temperature between about 50xc2x0 C. to 70xc2x0 C. Above this temperature, extensive tissue damage beyond the desired treatment site may occur as steam forms and ruptures tissue. However, to effectively ablate an arrhythmogenic site, individual lesions formed by adjacent electrodes must come together to form one continuous lesion that completely ablates an area of interest. If there are gaps in-between the lesions, they may not terminate the arrhythmia. By monitoring the tissue temperature, the physician is able to ensure that adequate heating is achieved so adjacent lesions meet or overlap to form as continuous a lesion as possible in view of the anatomical/geometric challenges presented. Such monitoring also allows a physician to avoid over-heating tissue which could cause the charring of the tissue and coagulation of surrounding blood.
To further avoid excessive temperatures, the device of the invention may also include fluid directing passageways which extend radially or longitudinally to facilitate delivery of cooling fluid. The temperature sensors may be thermocouples, although other suitable temperature sensors may be used, such as thermistors or other temperature sensing means.
The shaft of the distal section of the EP device is formed at least in part of individually-insulated electrical conductors that are electrically connected to individual electrodes on the distal section. Preferably the electrical conductors are braided. Individual wires in the distal shaft section are typically connected to temperature sensors, and, in the case of thermocouple temperature sensors, have a distal end which forms the temperature sensor. The temperature conductor wires may be braided with the electrical conductor wires. A plurality of polymer strands formed of nylon, DACRON(copyright) or the like may also be braided either with the wires or braided separately and incorporated into the sheath. Where an electrically hot tip is to be used in the catheter, the forming wire itself may be the electrical conductor. The proximal ends of the conductor wires are typically connected to individual pins of a multi-pin connector for energy and data delivery to whatever control unit and/or energy source the EP device is coupled.
The shaped end of the catheter will typically be straightened by a delivery sheath at some point prior to introduction into a guiding catheter. However, the EP device of the present invention may be constructed so as to be remotely manipulable into its desired shape using such structure as known to those with skill in the art, as for typical deflectable catheters. Also, the device may use a shape-memory alloy that assumes the desired shape when a preset temperature of the metal is reached. Naturally, such a device could be activated by heat of the body or by the application of electrical energy causing resistive heating of the material. To remove the device, especially where a preformed core member is utilized, the delivery or guide sheath may be used to once again straighten the device.
Depending upon its construction, the EP device of the invention may be used alone or with a variety of shaped or shapeable guide members. In one presently preferred embodiment, the EP device is used with a deflectable guiding catheter having a lumen which slidably receives the EP device of the invention and a distal section that can be deflected in either of two directions away from the guiding catheter longitudinal axis, such as a NAVIPORT(copyright) unit as described in copending application Ser. No. 09/001,249, filed Dec. 30, 1997, titled Deflectable Guiding Catheter to Qin, et al.
Once delivered through the inferior vena cava into the right atrium, the EP catheter is used by manipulating the device so as to hook the end of the device within the tricuspid valve of the heart. The end which passes into this region, whether it seats between cusps or not, serves as an anchoring portion when the surgeon partially retracts the catheter. This retraction puts tensile stress on the form of the EP device causing it to straighten somewhat. As it straightens, the interface portion of the catheter having electrodes is biased against at least a portion of the myocardial tissue of the isthmus. When in such close proximity, ablation may effectively occur. Preferably, this is performed by selecting only those electrodes in contact with the target tissue and applying RF energy to each (independently or in combination) and monitoring the temperature of tissue elevated by the heat generated as a result of the RF energy until a desired temperature is reached. Such steps may be carried out progressively by retracting or advancing the anchor region of the catheter to alter which tissue the interface region is biased against upon retraction. Further, upon complete retraction of the anchor region from the tricuspid valve, the hot tip may be placed into contact with tissue in difficult to reach recesses where upon RF energy is applied to ablate the tissue site and form a full, linear lesion made.
The catheter of the invention is configured for effective EP treatment of the isthmus region of a mammalian heart. This is to be achieved by a combination of the advantages provided by features of the catheter including, but not limited to, the shape of the catheter and placement of electrodes of the temperature sensors for monitoring of the lesion formation, and the RF active ablating tip disclosed. Ablation of the isthmus of a heart to treat atrial flutter and/or atrial fibrillation is further to be achieved by the method of manipulating the catheter as described herein.